Abstract:

Objective To isolate high efficient algicidal bacteria, and investigate their algicidal effect on Microcystis aeruginosa. Methods Bacteria were isolated from activated sludge, and were inoculated in Microcystis aeruginosa culture fluid. Algicidal bacteria were screened through observation of color of culture fluid and number of Microcystis aeruginosa. Algicidal efficiency was evaluated by calculating the algicidal rates, and high efficient algicidal bacteria were obtained. PCR was employed to sequence 16S rDNA of high efficient algicidal bacteria, and was aligned with the data of Genebank to identify the target bacterium. Transmission electronic microscopy was used to observe the morphological changes in the algae treated with algicidal bacteria for 48 h. Results A strain of algicidal bacterium was isolated from activated sludge samples, which was designated as N25-2 (hereinafter to be referred as N25). It was identified by 16S rDNA that the match rates of N25 with Bacillus SP. and Lysinibacillus fusiformis were both 99%. When the concentration of Microcystis aeruginosa was over 1×10⁶/mL and the concentration of bacteria reached 1×10⁶ cfu/mL, the algicidal rate was higher than 72% within 48 h. Transmission electronic microscopy revealed that there were increased vacuoles, deep staining of polyhedrons and increased phycobilisomes in Microcystis aeruginosa after being treated with N25, and the main morphological changes were plasmolysis and inner structural damage. Conclusion N25 has a high algicidal efficiency, and the algicidal mechanism may be associated with the secretion of bacteria, which needs further study.

Key words: algicidal bacteria, Microcystis aeruginosa, screen, identification